Past Paper Exam Questions

Question 1

Define the term standard enthalpy of formation.

Answer 1

→ the enthalpy change when one mole of a substance is formed from its constituent elements
→ with all products and reactants in normal states under standard conditions

Question 2

State why ultraviolet light is needed to produce free radicals.

Answer 2

provides energy to break covalent bonds

Question 3

Why is % yield important?

Why is atom economy important?

Answer 3

→ the higher the % yield, the higher the efficiency of converting reactants into products
→ a higher atom economy means less waste products and more useful product

Question 4

Explain why pentan-2-ol has a higher boiling point than pent-1-ene.

Answer 4

→ pentanol has hydrogen bonding
→ pentene only has weak VDW
→ hydrogen bonds are much stronger therefore require more energy to overcome

Question 5

Define stereoisomers.

Answer 5

molecules with same molecular formula but different arrangement of atoms in space

Question 6

What is a plasticiser?

Answer 6

a substance that is added to a material to make it softer and more flexible

Question 7

What is the effect of changing pressure on Kc?

Answer 7

no effect

Question 8

State the conditions for thermal cracking.

Answer 8

→ high temperature (around 500)

→ high pressure

Question 9

State the conditions for catalytic cracking. Name its products and uses.

Answer 9

→ slight pressure, high temperature, zeolite catalyst
→ produces branched & cyclic alkanes + aromatic hydrocarbons
→ (motor fuels)

Question 10

equation for fermentation of glucose

Answer 10

glucose → ethanol + carbon dioxide

Question 11

Write two propagation step equations to show the decomposition of ozone.

Answer 11

Cl ● + O₃ → ClO● + O₂
ClO● + O₃ → Cl● + 2O₂

Question 12

Describe how to make a volumetric solution.

Answer 12

1. Weigh the sample bottle containing the solid on a (2 dp) balance.
2. Transfer solid to beaker and reweigh sample bottle.
3. Record the difference in mass.
4. Add distilled water and stir with a glass rod until all the solid has dissolved.
5. Transfer to a volumetric flask with washings.
6. Make up to the 250cm3
   mark with distilled water.
7. Shake flask.

Question 13

Explain which molecule, ethanal or ethanol, has a higher boiling point and why.

Answer 13

→ ethanol - contains hydrogen bond (bc OH bond is polar)
→ ethanal - only contains VDW (there is no OH bond therefore no hydrogen bond)
→ hydrogen bond is stronger

Question 14

What does the are under the curve of the Maxwell distribution curve show?

Answer 14

total number of particles

Question 15

Give an equation for a reaction that removes nitrogen monoxide in a catalytic converter.

Answer 15

2NO + 2CO → N₂ + 2CO₂

Question 16

What is meant by the most probable energy on a MB curve?

Answer 16

the amount of energy that most particles have (the mode)

Question 17

State the reagents required to convert aldehyde into alcoholic nitrile.

Answer 17

• KCN
• dilute acid

Question 18

Explain how anti-bumping granules prevent bumping during reflux.

Answer 18

allows smaller bubbles to form

Question 19

State the reagent and condition for the formation of an amine from a halogenoalkane in two steps.

Answer 19

→ aqueous alcoholic KCN
→ H2 + nickel catalyst

Question 20

State why two liquids in an aqueous solution can be separated using a separating funnel.

Answer 20

Liquids are immiscible (don’t mix together)

Question 21

Explain why polymers do not biodegrade.

Answer 21

carbon-carbon bonds are non-polar therefore are not attacked by nucleophiles

Question 22

Give one reason why ethanoyl chloride is not used in the industrial synthesis

Answer 22

Corrosive OR forms strong acid/HCl

Question 23

Explain how carbon dioxide causes global warming.

Answer 23

→ C=O Bonds in CO2 absorb infrared radiation (of 2350cm-1)
→ IR radiation emitted by earth does not escape from
atmosphere

Question 24

State the meaning of the term complementary when it is used to refer to DNA strands.

Answer 24

(Complementary means the two strands must have base sequences)
that match (all) A to T and C to G

Question 25

Explain the bonding between two bases.

Answer 25

→ nitrogen & oxygen are very electronegative so C=O & N–H are polar
→ results in formation of a hydrogen bond between O and H
→ in which a lone pair of electrons on an oxygen atom is strongly attracted to δ+H

Question 26

Explain why simple alkanes/alkenes are not biodegradable.

Answer 26

→ no polar bonds
→ cannot be attacked by nucleophiles

Question 27

Explain why these practical steps are followed in a purification by recrystallisation experiment:
→ cooling flask to room temp before crystallisation
→ compressing crystals in the funnel
→ cold water poured through crystals

Answer 27

→ lower yield if warm
→ to ensure air passes through the sample, not around it
→ to wash away soluble impurities

Question 28

State why a minimum quantity of hot water is used in a recrystallisation experiment.

Answer 28

ensures solution is saturated to allow crystals to form

Question 29

Name three uses of phenylamines.

Answer 29

• making dyes
• making quaternary ammonium salts
• making (cationic) surfactants

Question 30

Give three reasons why TMS is used as a standard in 13C n.m.r. spectroscopy.

Answer 30

• inert
• low boiling point
• produces one single peak

Question 31

Reagent for the reduction of benzene into cyclohexane.

Answer 31

H2 (Ni / Pt)

Question 32

Bond angle in benzene and in cyclohexane.

Answer 32

→ benzene 120
→ cyclohexane 109.5

Question 33

Equation for concentrated sulfuric acid and concentrated nitric acid.

Answer 33

HNO₃ + 2H₂SO₄ → NO₂⁺ + 2HSO₄⁻ + H₃O⁺

Question 34

use for quaternary ammonium salts?

Answer 34

cationic surfactants